Generally, the conventional circular knitting machine employs a driving pinion to engage with a gear wheel, at the central portion of the latter there being no provision of shaft. Due to the clearance between the teeth of the pinion and those of the gear wheel, an oscillation would by all means be brought about. And each time when any of the latch needles rotates to the position where it is relatively most close to the oscillation source, the oscillation grows greater, whereas each time when any of the latch needles rotates to the position where it is relatively farthest from the oscillation source, the oscillation shrinks. Therefore, upon the surface of the knitted fabric, there would occur the undesired horizontal lines. Aside from the unequal oscillation, of course there are still another causes, such as the quality of yarns, the adjustment of cam etc which also would bring about the undesired horizontal lines. Nevertheless, these causes may more easily be controlled than the unequal oscillation and have hereinto been controlled. To prove that the undesired horizontal lines derive themself from the unequal oscillation, the inventor has taken the circular knitting machine of 38 gauge to make an experiment therewith. On the one hand, smear the dye on a yarn entrance of one transmission assembly which is most close to the oscillation source, i.e. the engagement point between a gear wheel and a pinion so that when the yarn is entered, the dye will be attached thereto. As a result, the knitted fabric reveal that there is the dyed track on the thick horizontal lines thereof. On the other hand, repeat the same experiment at another transmission assembly which is provided at the opposite position of said transmission assembly, the dyed track also is seen occurring on the thin horizontal lines thereof. To obtain a further proof thereof, the inventor removes the secondly mentioned transmission assembly and then finds that the thin horizontal lines disappear. Therefore, the fact finds itself true that the longer the oscillation goes, the denser would be the undesired horizontal lines.